This invention relates to highly active and stable ruthenium and osmium metal carbene complex compounds, their synthesis and use as catalysts for olefin metathesis reactions.
Transition-metal catalyzed C—C bond formation via olefin metathesis is of considerable interest and synthetic utility. Initial studies in this area were based on catalytically active mixtures consisting of transition-metal chlorides, oxides or oxychlorides, cocatalysts such as EtAlCl2 or R4Sn, and promoters including O2, EtOH or PhOH. For example, WCl6/EtAlCl2/EtOH 1:4:1. These systems catalyze olefin metathesis reactions, however their catalytic centers are ill-defined and systematic control of their catalytic activity is not possible.
Recent efforts have been directed towards the development of well-defined metathesis active catalysts based on transition metal complexes. The results of research efforts during the past two decades have enabled an in-depth understanding of the olefin metathesis reaction as catalyzed by early transition metal complexes. In contrast, the nature of the intermediates and the reaction mechanism for Group VIII transition metal catalysts have remained elusive. In particular, the oxidation states and ligation of the ruthenium and osmium metathesis intermediates are not known.
Group VIII transition metal olefin metathesis catalysts, specifically ruthenium and osmium carbene complexes, have been described in U.S. Pat. Nos. 5,312,940 and 5,342,909 and U.S. patent application Ser. Nos. 08/282,826 and 08/282,827, all of which are incorporated herein by reference. The ruthenium and osmium carbene complexes disclosed in these patents and applications are of the general formula

where M is ruthenium or osmium, X and X′ are anionic ligands, and Land L′ are neutral electron donors.
U.S. Pat. Nos. 5,312,940 and 5,342,909 disclose specific vinyl alkylidene ruthenium and osmium complexes and their use in catalyzing the ring opening metathesis polymerization (“ROMP”) of strained olefins. In all of the specific alkylidene complexes disclosed in these patents, R1 is hydrogen and R is either a substituted or unsubstituted vinyl group. For example, a preferred vinyl alkylidene complex disclosed in these patents is
where Ph is phenyl.
U.S. patent application Ser. Nos. 08/282,826 and 08/282,827 disclose specific vinyl alkylidene ruthenium and osmium complexes and their use in catalyzing a variety of metathesis reactions. The catalysts disclosed in these applications have specific neutral electron donor ligands L and L1; namely, phosphines in which at least one substituent is a secondary-alkyl or cycloalkyl group. As in the above U.S. patents, in all of the specific alkylidene complexes disclosed in the patent applications, R′ is hydrogen and R is either a substituted or unsubstituted vinyl group. For example, a preferred vinyl alkylidene complex disclosed in these patent applications is
where Cy is cyclohexyl.
Although the vinyl alkylidene complexes disclosed in the above patents and patent applications exhibit high metathesis activity and remarkable stability towards functional groups there are at least two drawbacks to these complexes as metathesis catalysts. First, the preparation of the vinyl alkylidene complexes requires a multi-step synthesis; and second, the vinyl alkylidene complexes have relatively low initiation rates. Both of these aspects of the vinyl alkylidene complexes are undesirable for their use as metathesis catalysts. The multi-step synthesis may be time consuming and expensive and may result in lower product yields. The low initiation rate may result in ROMP polymers with a broad molecular weight distribution and prolonged reaction times in ring closing metathesis (“RCM”) reactions.
For the reasons discussed above, there is a need for well-defined metathesis active catalysts that have the following characteristics: first, they are stable in the presence of a wide variety of functional groups; second, they can catalyze a variety of metathesis reactions including the metathesis of acyclic and unstrained cyclic olefins; third, they have a high initiation rate; and fourth, they are easily prepared. Furthermore, there is a need for olefin metathesis catalysts that can catalyze the ROMP of strained and unstrained cyclic olefins to yield polymers of very low polydispersity (i.e., POI=1.0) and that can catalyze the RCM of acyclic dienes with short reaction times.